Simplify the following expression: $a = \dfrac{1}{9n} + \dfrac{1}{6n}$
In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $9n$ and $6n$ $\lcm(9n, 6n) = 18n$ $ a = \dfrac{2}{2} \cdot \dfrac{1}{9n} + \dfrac{3}{3} \cdot \dfrac{1}{6n} $ $a = \dfrac{2}{18n} + \dfrac{3}{18n}$ $a = \dfrac{2 +3}{18n}$ $a = \dfrac{5}{18n}$